1. Field of the Invention
The present invention relates to a method for coating or printing on a textile by applying thereto a water-free, energy-curable, polymer-forming composition, especially useful as or in a coating or ink, the composition containing an epoxy oligomer, and an alkoxylated polyol monomer.
2. Background of the Art
Printing inks generally are composed of coloring matter such as pigment or dye dispersed or dissolved in a vehicle. The ink can be a fluid or paste that can be printed onto a substrate such as paper, plastic, metal, or ceramic and then dried.
Inks can be classified according to the substrate onto which the ink is intended to be applied or the method of application. For example, inks can be applied by raised type (e.g. letter press, flexographic), from a planar surface (lithographic), from a recessed surface (intaglio) or through a stencil (silk screen). Different methods of application and different substrates require different properties in the ink.
In silk screen printing, the ink is forced onto a substrate through a stencil, or "mask", having a porous screen area configured in the shape of the indicia to be printed such as letters or graphics. The substrate can be paper, textile, metal, ceramic, polymer film, and the like. The screen can be a gauze or mesh fabricated from metal, silk, or various polymer materials.
The mask is generally prepared by coating a screen with a curable composition, curing the composition, and then engraving indicia on the screen. The engraved areas are porous, thereby permitting ink to be forced through the screen onto the substrate to print the indicia.
After printing, the ink on the substrate is cured or hardened by any of several methods such as, for example, exposure of the ink to heat or radiation (e.g. ultraviolet, electron beam, and the like), evaporation of a solvent in the ink composition, or oxidation hardening of drying oil components (e.g linseed oil, tung oil), and the like.
Apart from printing, coatings can also be applied to substrates for purposes of surface modification. For example, coatings can be applied to textiles to improve color fastness, water repellency, or other properties.
The three main technologies being practiced today which make up the bulk of the coatings and inks include solvent borne, water borne, and zero volatile organic compounds (VOC). Solvent borne and water borne systems produce inks and coatings which, in their uncured state, are washable. Water washability is a desired feature of the coating composition since the coating application equipment needs to be cleaned for reuse. However, there has been a technological push to eliminate organic solvents and water as components in the ink or coating composition. Organic solvents present environmental health concerns. And both solvent based and water based systems are energy intensive, requiring drying ovens to remove the solvent or water. For example, thermally induced drying and curing of coated screen fabric typically requires about 7,000 to 12,000 kilojoules of energy per kilogram of fabric as well as a long curing time, typically several hours.
The use of textiles as a substrate for printing and coating presents additional problems. For the past two decades considerable efforts have been made to develop energy polymerizable screen printing inks for fabrics. One desired property of an ink or coating applied to textiles is that the ink or coating adheres firmly to the textile. For example, a poorly adherent ink will not have the requisite color fastness or abrasion resistance and may degrade under normal wearing and washing conditions. A high degree of crosslinking enhances abrasion resistance and color fastness, and facilitates the grafting of the ink onto the fabric. However, another desired property is that the ink or coating be flexible. With a stiff ink or coating the textile loses the tactile properties, or "feel," of the original fabric. Low crosslinking produces soft, flexible films. Consequently, what is desired is a method for printing or coating a textile with a waterless, zero VOC composition wherein the treated textile retains its original feel while exhibiting good color fastness and durability of the ink or coating.